Fuel mileage dropped drastically overnight-help!

Has anyone else had any issues with their fuel mileage just dropping all the sudden and staying there. move got a 3in lift of 35s, so naturally I’ve lost some fuel mileage but I was averaging 15.5 mpg for the last 6 months or so. I town my 1500lb side by side on an 8 hour trip and averaged 12.5 miles a gallon. Okay, fine no problem. On the way back home I started averaging 8.5 8.8 got up to 10.8 or near there. Now even without the trailer I’m sitting around 12.5-13.3. Same fuel same everything. Checked my air filters, tire pressure you name it. Is this maybe a turbo issue?? No check engine lights.

 

To Colorado TJ and you. I have calculated by hand. Not done a spedo cal. The computer is what made me start doing it by hand. It’s within the computer mpg average by a few then a here or there. Just couldn’t imagine how all the sudden with absolutely no changes to anything, it drops average 3-4mpg and sometimes even more. “Normal driving conditions” cruse control on 60mph or just driving normally. Etc etc

 

So I stared here in Atl and drove down to Tampa Florida. Then towing around in Florida during the holidays I started having the massive drop. Chalked it up to towing The sxs but then while not towing it still sucked and has stayed that way. Of course I’ve cleared all mpg history and all that on the computer just to start from a clean slate. Still the same.

 

I’m lost at this point. I don’t dare even consider asking the dealer, I know they’ll be absolutely no help. I’ve check my air filters, hoping on the 1% chance there’d be a plastic back in one of them or something, but no. Unplugged the negative cable for about a minute. But I’ll try 10 mins.

 

I’ll give er a shot. Idk what else in the world it could be.

 

Ill ask the stupid question. Did you reset your MPG readout prior to driving after towing? If not, it is still averaging the ~8MPG you got when you were towing. I tow a 23.5 foot boat and always reset my MPG gage to make it more realistic.

 

Sometimes it’s wind or grade that causes big differences in fuel economy on the same route.

 

Try non-ethanol fuel, winter fuel tend to have more ethanol (up to 10%) and it can be lot less efficient than ethanol free fuel, usually I see quite bit mpg drop in winter when they switch to higher ethanol blend, then it quickly returns to normal after one or two tank of ethanol free fuel.

FYI, you have higher chance to find ethanol free on octane 91.

 

Yeah I took that into account. Did it both ways, and still up here at home now too. Hard to say what’s going on.

 

I’ll check it out, and all your guys tips are good tips. But I can’t find a reason for the sudden 4 or so mile mpg drop. That’s huge.

I’ve heard non-ethanol burns a lot whats up Omer, but I’ve never really looked into it. I’ll give it a try. I’m sure there’s some near me somewhere

 

Dumb question. Are you sure your parking brake is fully released?

 

Yeah I did. On the way down it was good relatively speaking. From 15.5 to 12.5-13. It was later during the trip it just dropped drastically. And now still does even with no trailer. I’ve reset all the trip and mpg gauges. Tried to reset the ecu by unplugging it 10 mins not sure if it did or not.

 

I hope so, it’s electronic. It either is or isn’t, as far as pressing the button. But you’d think it’s something like that to drop 4mpg. It’s something major or a bad ecu read out. A little tire pressure or a dirty air filter etc etc (which neither I have) would drop 4 mpg.

 

Does the exhaust smell rich cold? Warm?

an engine is a pump, and this fancy efi only uses the fuel to satisfy the requested power. Make sure your brakes or pulleys arent dragging. You better believe i see the irony of a dude with a lift and 35's whining about fuel milage. Whats your tire PSI?

 

Believe someone on here had a sticking rear caliper, not sure if it was the main or parking brake. A temp gun after a drive would reveal the difference in hub temps if that was the case.

 

I’m not whining about fuel mileage as that I’m not getting what everyone else is getting. It’s that I’ve had the lift and tires for 6 months and ALWAYS been at 15.5 then all the sudden it’s 10-11 with no change. Exhaust smells the same. No hot wheels or calipers. No check engine lights. No new sounds or feelings when driving or idling. Wondering if every little problem with the turbos would through a code or not.

tire psi is right at 40

 

You sure this is not a uphill into the wind difference? My 2.5gen averages mid 20s driving from my moms house to my house, but mid teens on the way back.

 

Positive. Same rounds I’ve been driving since I got the truck.

 

I didnt mean nothing by it. When i drag my truck down to 16 i curse myself, and promise to drive easier next time. I had an instant mpg gauge in my moms sequoia, learned that killing overdrive below 60 saved lots of fuel. Whats peak torque start at 1500rpm? Do the math and see which gear is happiest at 1500 rpm. Maybe whatever lockup is. Thats my theory on why the other guys sequential mode defaults to whatever gear locks up. (nissans have a rev matching thing), my moms newer qx80 drops to whatever gear is in lockup at whatever speed, (i use engine braking as much as necessary) and it'll be 6th or 7th depending on who i settle behind 60-70mph, the titan doesnt offer OD in sequential mode, but i would love to run a toggle or flappy paddles on my tundra to give me control of the solonoids, instead of an OD button and shift lever.

 

OP, how's the rpm while cruising? I'm just wondering if the transmission if shifting all the way to 10 and not getting stuck to 9 or 8. Did you notice a change of rpm after the towing? How about turbo boost? Did you notice any change in boost or if the turbo stay in boost in more time than before the tow? Really curious about this.
Have you disconnected the battery for a few minutes to reset everything? Not sure if it will work but maybe worth trying.

 

I’m gonna guess sticking caliper or parking brake. Or maybe your trans isn’t going into the overdrive gears. Something isn’t right. That’s a drop of 30-35%.

 

The difference in mileage difference on the return trip from Tampa to ATL is not surprising, you are going uphill. Where did you get gas?, have you run thru the tank with the "low mileage yet".

 

May be a dumb question but just trying to rule stuff out with everyone else. Are you using remote start more than you were? Idling with remote start dropped my mpg average 2-3 mpg.

 

No I’m up for all questions. I’m hoping there’s an “ahha moment” but I’m not sure there will be haha.

No I actually use it a lot more in the summer when it’s hot, than now. But even then never noticed a drop in mpg. I use it time to time now, but not often.

 

How do you calibrate the speedometer?